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Continuous vs Programmable watt rating...

#41
Hi.

Wow, it's been over a week IIRC since the last over/underpowering - DC in the signal - square waves destroy speakers - thread.

If someone believes in something, that's their loss (often a financial one too), but to endlessly argue with people who can be called experts and tackle with these things in daily basis, that's just plain silly not to mention ignorant. IMHO of course.

Regards
Sam
 
#43
Hi.

My comment above wasn't directed towards You B-string. I apologise if it seemed that way. It was directed towards the people who won't read the FAQ about the subject and cling to misinterpreting documents and texts.

As for Your question about the DC "duty cycle", less is good, and design can improve things, but a certain DC component is everpresent in dynamic signal. While it's in the millivolt range, it goes un-noticed. Mainly because almost every amp I have tested/measured has the idle DC component in the output (mV-range) anyway.

The MI amps I've tested, not a single one of them have been able to reproduce square signal with any kind of accuracy above 1/2 of the max output power rating. The power supply section (caps) just doesn't keep up and either the leading edge or both start to curve. Hi-Fi amps are a totally different matter, but they have their limit too.

For me the square wave argument ends right there, if the amp isn't capable of reproducing square wave, how can it create one?

Regards
Sam
 
#46
B-string said:
If I missed the answer to my question I am sorry. I am looking for an answer other than I said so.
Click to expand...

Frankly those who really want answers, deep knowledge... are best served really going beyond any bassplayer forum. I've seen tons of people over the years claim they really want to get jiggy with knowledge. But forum hangers never really seem to learn more, they often at best regurgitate, often with manglements, which is why discussions often are circular on even the most basic stuff.
 
#49
bongomania said:
No, I was specifically referring to the quote posted earlier in this thread.
Click to expand...

I pity companies in that regard. There are no shortcuts to understanding things fully yet the companies must often try to do that with the potential and actual customers who are generally kinda into fast food learning more than they are nutrition.

Peavey is pretty good about more detailed tech info in White Papers and at least used to be in their Monitor Magazine.
 
#52
In my opinion, with all this amp power versus speaker power.

If you were going to build a foolproof combo, where there is not any external speaker connections. And you wanted to deliver the maximum wattage to the internal speaker, then you'd want to have a speaker rated for twice the amplifiers power at the speakers impedance. With this, even at full distorted clipped power you wouldn't have enough power to fry the speaker with all the knobs turned fully up.

If it was a PA/sound reinforcement/FOH, something with vocals or micing instruments, a system you'd be sensitive to when it distorted. A system that includes midranges and tweeters, and you absolutely wanted to get maximum undistorted SPL levels. The JBL's and Peavey's recommendations kick in. These systems aren't foolproof and expect some common sense - you hear distortion - turn it down.
 
#53
...Peavey back in '89 and '90 had these cool Dynamic System Controllers tailored for a variety of their enclosures. These processors had a speaker-level feedback loop going back into them from the power amp outputs, that as voltage rose, the Controller moved the woofer's 5th-order high-pass filter from 38 Hz to as far as 58 Hz, thus limiting the chance of overexcursion as levels climbed. They also had dynamic LF loudness contouring that could be used not at all or mildly or quite dramatically that at low levels applied lots of LF EQ inverse to the LF section of the Equal Loudness Contour, and as levels climbed, would back this EQ off.

Any combo that had this would cost more, but sure would provide protection and fidelity. I wonder if this isn't a little bit of what Roland might be doing in their D-Bass combos.
 
#54
What ever you do to make an amp foolproof someone's going to undo it. You put a fuse in to protect a circuit from damage when something fails and some genius will wrap it in foil to get the amp "working" again. If you build it someone WILL abuse it and then blame you for the disastrous results. How many utterly stupid actions have you read about on this forum alone? All techs have seen the results of user "intervention".

Paul
 
#55
BassmanPaul said:
What ever you do to make an amp foolproof someone's going to undo it. You put a fuse in to protect a circuit from damage when something fails and some genius will wrap it in foil to get the amp "working" again. If you build it someone WILL abuse it and then blame you for the disastrous results. How many utterly stupid actions have you read about on this forum alone? All techs have seen the results of user "intervention".
Click to expand...

...And thus the "Hi! I'm your friendly amp technician!" trouble-shooting questionnaire was begot ; }
 
#56
Bassmec said:
So its your considered opinion that the owners of 100 watt tube amps can feel perfectly secure and reliable and well equipped with just one of these:
Invalid Link Removed
Sure you haven't been smoking them!:D
I think it would take much of my rehearsal studio customer list about a couple of Brutal Truth covers to have the voice coil nicely melted and blistering.
If you worked for Marshall you would be recommending a minimum of 4 Celestion speakers at a total handling of three times the total amp output in watts RMS.:ninja:
Click to expand...

He's not saying that at all. You're talking two very different applications. That 100W tube amp, when driven well into clipping would probably put 150W+ into the speakers (possibly close to 200W). Since guitar amps are intentionally used this way, it makes sense to have your speaker system rated at twice that of the amplifier. In the PA world, where distortion is not desirable, the 2X rating allows you to get maximum SPL out of the speaker system without distortion.



hrgiger said:
I realize that but from other articles I've read, DC is in the signal. I read that "the "flat top" of the signal simulates a DC signal..."

Also for example in this paper : Link Removed, I read that basses produce assymetrical waveforms:

Sources of Asymmetrical Waveforms

Most people probably tend to think that their music signal is relatively symmetrical, and this is usually true when averaged out over a long period (perhaps 30 seconds or more). However, there are a great many sources of asymmetry within the programme material itself, and these include ...

* Human voice (spoken or singing)
* Wind instruments (flute, horns, reed instruments, etc.)
* Plucked and struck stringed instruments (guitar, harp, piano, bass, etc.)

And then I read in this same paper that:

There is no doubt that a clipped asymmetrical waveform will generate a DC component in the output of an amplifier.

So I gathered that a bass guitar signal that is clipping will have some DC in it, which is in other words, a "squarewave type waveform" which can damage the voice coil. Is this incorrect?
Click to expand...

What you're missing here is that an unclipped asymmetrical waveform has this DC component as well and assuming that the amp in question is competently designed and clips symmetircally it's the same whether the amp is clipping or not. This is decidedly not the same thing as a squarewave-type waveform, it just means that the average signal level is non-zero. The DC components of these signals are typically small enough to be inconsequential.

If you look at one period of a perfect squarewave you'll see that the portion of the signal above the zero line is equal and opposite to that below, hence the average level is 0, so the perfect square wave has no DC component.

As for considering the flat tops of the waves "DC," this myth is born in reality, because a square wave has the same heating power as a DC signal of the same amplitude. But that's where the similarities to DC end. Anything that has a discernible alternating pattern around a zero axis is not considered DC.
 
#57
B-string said:
The question is meant to envoke thought. As in at power up and power down a DC supply with the rise and fall it is no longer DC? At what time constant is a given voltage concidered AC or DC? Automotive applications use a rectified AC generator, when that AC componet exceeds a given point, systems are affected and finally the battery fails to charge. Still concidered a DC system even though properly operating it contains AC ripple of changing frequency and non "constant" voltage. If we are going to split hairs lets have some fun with it? :)

Or not? :ninja:
Click to expand...


I would venture that any signal that has a discernible regular alternating pattern around a zero axis would not be considered DC, even though in some cases it may have a DC component.

An amp's power supply would primarily be DC despite the power up and power down variances and ripple because under normal operating conditions the power supply would have a very small AC component relative to the DC component. A couple of mV of AC ripple on a power supply rail would be swamped by the 10s of volts DC component.

In a cosmic sense, there's no such thing as DC unless there's an unwavering DC signal that began when the universe did and will continue until it ends. :ninja:
 
#58
Nice disscussion going on here!
I had a long post prepaired when IE crashed so I'll cut it short.
We can safely put to rest that a clipped or "flat topped" signal is NOT a squarewave. If you expand a "flat topped" portion on an oscilliscope you will find it is not "flat" but modulated by harmonics and even AC ripple if it originated from the output stage.
The "Net effect being zero" I can't subcribe to as that would imply no time shift between peaks. A voice coil will produce just as much heat from a negative peak as a positive one.
My contention here is; If these "waves" are being produced within the Xlim of a driver the heat should be handled by driver design. If you use effects in your Bass signal chain and ask for high power that runs the drivers at or very close to Xlim that heat can be distructive (user abuse). In this case expect lower power handling than "rated".
Don't blame an amp or speaker if you drive it harder than it was designed, the speaker being the weakest link.
The caviot is Bass frequencies not higher faster frequencies like from guitars although they are not exempt from heat stress, just to a lesser degree.
 

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